Setting up the logging on all the cache events also helps debugging on for example IPad where all you have to rely on is the console log. This blog post shows how to set things up.

Also, something I ran in to on the IPad you might have to shut down all web applications on the IPad before refreshing your application with a Cache manifest. The symptom is that all files are downloaded (shown with progress events) but when its done the IPad just gets an error message. If this is the case, just shut down all web-applications and Safari and reset the Cache from the settings. That got it working again.